1. Field of the Invention
The present invention relates to a method for controlling track jumps of an optical pickup. More particularly, the invention relates to a method for controlling track jumps of an optical pickup incorporated in an optical disc apparatus by controlling the optical pickup in fine-tuned fashion such that the optical pickup is moved rapidly and accurately to a target track without suffering from any effects of disturbances such as scars on the disc the track jumps.
2. Description of the Related Art
The optical disc apparatus referred herein is a data reproducing apparatus that reproduces recorded data from an optical disc, or is an apparatus that records and reproduces data to and from an optical disc.
A typical optical disc apparatus is outlined below with reference to FIG. 6. FIG. 6 is a block diagram showing an overall structure of an optical disc apparatus.
As illustrated in FIG. 6, the optical disc apparatus 20 basically comprises: a spindle motor 2 for rotating an optical disc 1; an optical pickup 3 for irradiating a laser beam to the optical disc 1 upon data recording or reproduction; a dual-axis mechanism 4 for getting an actuator to displace an objective lens 3a of the optical pickup 3 radially across the optical disc 1 and in a way approaching and leaving the disc 1; a sled motor 5 for moving the optical pickup 3 radially across the optical disc 1; and a magnetic head, not shown, for applying a modulated magnetic field to the optical disc 1.
The optical disc apparatus 20 further includes a recording and reproducing circuit 6. The recording and reproducing circuit 6 processes video and audio signals coming from the optical pickup 3 according to predetermined formats and sends the processed results to the outside. These data are also fed back to the optical pickup 3.
In addition, the optical disc apparatus 20 comprises a servo processing circuit 7, a first driving circuit 8 and a second driving circuit 9 as control systems.
The servo processing circuit 7 analyzes reflected light signals that are detected by the optical pickup 3 from the optical disc 1. In so doing, the servo processing circuit 7 detects a focal point on the optical disc 1 of the laser beam irradiated by the optical pickup 3, as well as a relative positional relation between the laser beam and the irradiated track.
Through the first driving circuit 8, the servo processing circuit 7 then supplies a focusing control unit of the dual-axis actuator 4 in the optical pickup 3 with a control signal FOUT for controlling the focal point to within a predetermined range, and feeds a tracking control unit of the dual-axis actuator 4 in the optical pickup 3 with a control signal TOUT (tracking drive signal) for controlling to within a predetermined range the relative positional relation between the laser beam and the irradiated track.
Through the second driving circuit 9, the servo processing circuit 7 also supplies a control signal SOUT (sled drive signal) for moving the optical pickup 3 in accordance with the amount of shift made by the objective lens of the dual-axis actuator 4, to the sled motor 5 that moves the optical pickup 3. The servo processing circuit 7 thus moves the optical pickup 3 as a whole in accordance with lens moved by the dual-axis actuator 4, whereby so-called tracking control is effected for track follow-up.
Furthermore, the servo processing circuit 7 obtains through the second driving circuit 9 a detected speed value from a speed sensor 10 detecting a moving speed of the optical pickup 3. With the speed value acquired, the servo processing circuit 7 supplies the second driving circuit 9 with a control signal SDCNT (sled feed voltage) for controlling the moving speed of the optical pickup 3. This allows the optical pickup 3 to move (i.e., track jump) smoothly at the suitably controlled moving speed.
Described below with reference to FIGS. 7A through 7D is how track jumps of the conventional optical pickup 3 are typically controlled. FIGS. 7A through 7D show timing charts of signals involved in the control of track jumps of the optical pickup.
An initial motion sled kick pulse Kick D indicated by waveform in FIG. 7C is first fed to the second driving circuit 9 to start driving the sled motor 5 in a desired direction. The sled motor 5 is firstly driven so as to absorb elements of delay caused by inertia upon starting as well as by the initial motion sensitivity and static friction of the motor.
An initial motion tracking kick pulse Kick F indicated by waveform in FIG. 7B is then supplied to the first driving circuit 8 to drive the tracking control unit of the dual-axis actuator 4 in the optical pickup 3, whereby driving the objective lens 3a of the optical pickup 3 in a desired direction.
A detected signal of reflected light output from the optical pickup 3 is analyzed to find illustratively the difference in reflectance between tracks and non-track portions on the recording surface of the optical disc. Such analyzing process yields a tracking error (TE) signal representing the relative positional relation between the laser beam and tracks as indicated by waveform in FIG. 7A.
Counting zero-cross (TZC) points of the tracking error (TE) signal provides the number of tracks traversed by the optical pickup 3 in track jumps. Then, in accordance with the number of jumped tracks, a control signal SDCNT for controlling a target moving speed of the optical pickup 3 is adjusted as indicated by waveform in FIG. 7D. In addition, a tracking kick voltage is applied to a tracking actuator so as to control the track jumps of the optical pickup 3, thereby allowing the optical pickup 3 to reach a desired track.
As outlined above, the optical pickup is conventionally controlled in track jumps using control signals based on a number of factors: constant time intervals, a predetermined voltage level, or a variable voltage signal, all associated with polarity inversion between starts and stops. However, each of these control signals is determined on the basis of the result of the immediately preceding single track jump, so failure to measure that particular track jump triggers the output of erroneous kick pulses, leading to unstable control of the optical pickup.
The conventional method is thus limited in controlling capability and has had difficulty in providing high-speed access to the target track.
Furthermore, not only being poor in accuracy on jump performance, the conventional controlling method for the optical pickup exhibits tardy recovery from unstable jumps caused by scars or smears on the disc surface, leading to a jump error in some cases, thereby making it impossible to reach the target track.
The present invention has been made in view of the above circumstances and provides a method for controlling track jumps of an optical pickup in gaining high-speed access to a target track freeing from any effects of disturbances.
When devising the present inventive schemes, the inventors of this invention studied the conventional method and came to the conclusion that; the conventional speed control type method for the optical pickup exhibits its poor control capability ascribed to the process of determining the following control signal based on the result of the preceding single track jump, regardless of whether the control voltage or pulse width of the control signal was fixed or variable. The solution proposed by the inventors to the deficiency above is as follows:
Illustratively, time intervals of TZC (tracking zero cross) signals are continuously measured for comparison between a target time and a measured time. The difference therebetween is computed as an error, and a control signal with a voltage or a pulse width representing the magnitude of that error is output to the actuator of the optical pickup. For control of the driving speed of the actuator, the comparison between target and measured times should take into account not only a time difference regarding a single preceding track but also time differences with respect to a number of the previous track jumps. These time differences are then illustratively averaged so as to yield a mean value which is used as a basis for generating a control signal.
Accordingly, even using a disc in which track pitches vary for several tracks and the tracking error signal may contain so many noise elements that TZC intervals are widen or narrowed abruptly as if the TZC signals were chattering, the inventive method still allows the actual speed to be measured without error so as to ensure reliable jump motions.
In achieving the foregoing and other objects of the present invention and according to one aspect thereof, there is provided a method for controlling track jumps of an optical pickup in an optical disc apparatus for recording and reproducing data to and from an optical disc, wherein the optical pickup is moved to a target track of the optical disc comprising the steps of: when the optical pickup has jumped to a single track located halfway between a current position and the target track; computing a speed difference between a target jump speed set for the single track and an actually measured jump speed over the single track; outputting one of an acceleration signal, a deceleration signal and a speed maintaining signal representing the magnitude of the speed difference between the target jump speed and the measured jump speed as a control signal for controlling the speed for the optical pickup to jump to a next track immediately following to the single track;
adjusting the jump speed difference with respect to the single track based on at least one of speed differences between the target jump speed and the measured jump speeds regarding a plurality of tracks jumped previously to the single track, and by resorting to predetermined relational expressions; and
outputting one of the acceleration signal, deceleration signal and speed maintaining signal on the basis of the adjusted jump speed difference as a control signal for a track jump to the next track.
According to the present invention, using too many tracks for adjusting the speed difference may level out control signals, resulting in poor accuracy. In practice, about three tracks are preferred, i.e., one track plus the two tracks preceding thereto.
Preferably, the method further comprises the step of computing the speed difference between the target and the measured jump speeds based on time intervals of a track jump zero cross signal.
In another preferred variation of the invention, the method further comprises the step of outputting a pulse signal having a variable pulse width as a control signal such that:
(1) if the adjusted speed difference is positive, with the measured jump speed higher than the target jump speed, the jump speed of the optical pickup is decelerated in proportion to a magnitude of the speed difference;
(2) if the adjusted jump speed difference is negative, with the measured jump speed lower than the target jump speed, the jump speed of the optical pickup is accelerated in proportion to the magnitude of the speed difference; and
(3) if the adjusted jump speed difference is zero, with the measured jump speed equal to the target jump speed, the jump speed of the optical pickup is kept unchanged.
In a further preferred variation of the invention, a pulse signal having a variable pulse voltage may be output as a control signal, upon carrying out the three controlling steps above.
As outlined, the inventive method for controlling track jumps of the optical pickup involves acquiring speed differences between target and measured jump speeds from track jumps over a plurality of tracks, and supplying a tracking actuator and a sled motor with control signals reflecting the acquired speed differences between the target and the measured jump speeds for speed control. This permits accurate track jumps of the optical pickup over the disc surface regardless of disturbances.